In pick-and-place machines, it is conventional to provide a number of magazines of a variety of very small, thin, chips, such as resistors and capacitors, which present the chips at pick stations from which they are removed and then incorporated in the electronic circuit being constructed by the machine. It has been common practice to provide rather complex and expensive arrangements for feeding the chips to the pick stations and locating the chips at such stations. One such arrangement involves positioning a magazine beneath each pick station, each magazine having its own logic and driving circuit in an attempt to assure that a part is always presented at the top of the magazine. The resulting construction is undesirably complicated and expensive, and may lack reliability and ruggedness.
A highly desirable method of feeding chips to pick stations is by means of a vibrating table, there being rows of chips disposed in parallel grooves in the table. Vibratory feeding of the chips toward the pick stations is thus effected until a stop bar is reached, but it is at the stop bar that critical problems arise. It is emphasized that the chips are very small, and usually are not perfectly rectangular. When such chips are vibrated toward a stop bar that is fixed in space, and when a chip is against a stop bar, the one pushing behind it tends to slide underneath to create a "shingling" effect, or to tilt up the first chip at a 90-degree angle. Reliability and pick accuracy are thus substantially degraded. The tendency to shingle is exacerbated because the stop bar is fixed in space, hence the chip against the bar is not moving. However, the other chips in the component feed tray are vibrating against the fixed chips and tend to slide underneath.
When the stop bar is not fixed in space, but is instead mounted on the vibrating table, the tendency toward shingling is somewhat reduced. However, other problems are not diminished, one being that when only one chip is in the pick station, it tends to vibrate against the stop bar and then bounce away from it, again degrading the accuracy of the pick position.
The tendency toward shingling is increased, even when the stop bar is mounted on the vibrating table, when certain magazine and actuator arrangements are employed which cause cessation of chip loading into the grooves when the grooves are full. The full grooves, in combination with the actuator means to unload the magazines, create low forces--additional to the vibratory forces--which push the rows of chips against the foremost chip and tend toward shingling.